While the age old idiom warns of “seeing the forest for the trees,” we’re here to warn of the opposite: “seeing the trees for the forest!” What we mean is that it can be difficult to notice the difference between invasive and native species in our forests; many invasive species look quite similar to native species. However, if you know what to look for, you’ll start to notice the differences with ease! Below we outline some of the common invasive plant look alikes you might run into during a forest stroll.
This article can serve as a guide for plant identification, differentiating native from non-native species while weeding, and for planting look-alike alternatives to invasive species. If you are planning to replace your laurel or holly with something like a rhododendron, make sure the conditions are appropriate!
Some of the comparisons below contain multiple species on the native or invasive species side, make sure to check for multiple images!
Throughout the year, evergreen and deciduous shrubs provide an important source of food and shelter for all sorts of wildlife. While invasive, weedy shrubs can also provide food and shelter for wildlife, they tend to create dense, monocultural stands. These dense stands block out native plant species, giving local wildlife fewer options, and ultimately preventing many animal species from thriving. Reclaiming and restoring green spaces that have been dominated by species like Himalyan blackberry is key to having healthy forests in the future! But before we can clear weedy species, it’s key that we know the difference between native shrubs that need our help, and invasive species that are taking up too much space.
While the berries of this invasive shrub are a favorite for many birds, those same birds have spread English holly throughout PNW forested lands. As holly spread, it displaces native shrubs and trees which provide a more balanced diet for local wildlife.
Tall Oregon Grape
People frequently confuse English holly with tall Oregon grape, which also has sharp, evergreen leaves. However, tall Oregon grape has opposite leaves where English holly has alternate leaves. Additionally, tall Oregon grape has bright yellow flowers in early spring and blue-purple berries in the summer.
Low Oregon Grape
Also known as dull Oregon grape, this native shrub is also frequently confused for English holly. Low Oregon grape have softer and duller leaves than holly or tall Oregon grape, and thrives better in shade conditions than either. Low Oregon grape also has opposite leaves.
Laurel is a favorite in landscaping, particularly for those seeking privacy. While its dense leaf growth is a plus for many private landowners, this shrub’s aggressive growth is a huge headache for land managers. Laurel is a challenging shrub to remove once established, and typically requires herbicide treatment.
Rhododendrons are famous for their showy, colorful flowers. Pacific rhododendron flowers in late spring, and is a delightful native shrub that can form extensive layers with enough sunlight. The Pacific rhododendron is also the state flower of Washington! Rhododendron tends to have more pointed leaves, that are less waxy than laurel.
Perhaps the greatest bane of all restoration practicioners, Himalyan blackberry is an aggressive spreader with large thorns, capable of growing in a variety of conditions. While of course the berries are delicious, Himalyan blackberry is a large barrier to restoration of functioning ecological habitats in the PNW.
Himalyan blackberry is identifiable by its leaves which have 3-5 palmate leaflets. Stems are green
but often with a reddish tinge. The big thorns are hard to miss!
Cutleaf blackberry is also non-native, but not as invasive as its relative, Himalyan blackberry. It is easily distinguishable from Himalayan blackberry due to its namesake: the “cut” leaves. The leaves are distinctly more lobed and textured than the large, undivided leaves of Himalyan blackberry.
Photo by Rasbak
Trailing blackberry, like their name suggests, tends to trail along the ground, and appears more like a vine than a shrub. Trailing blackberry is distinguishable from Himalyan blackberry via its ternate (three leaflet) leaves, and distinctly blue-green stems. The thorns are also smaller and more gentle!
Photo by Kirill Ignatyev
Salmonberry is another native species that frequently is confused with Himalayan blackberry. The thorns on blackberry are generally larger and more curved. If you look closely, you can see that Salmonberry has clusters of three leaves, with two leaves that are lobed to make it look like five leaves.
Herbaceous (non-woody) plants typically grow shorter than shrubs, and exist primarily on the forest floor. These flowering plants provide nutrients and moisture for soil, in addition to providing for pollinators during the flowering season. Herbaceous species also include a great variety of species and forms. This great diversity of forms can create a difficult situation for those looking to id plants, particularly when these plants aren’t flowering! Below are just a few key look-alikes to look out for.
If you live by a river or stream, odds are you’ve seen Japanese knotweed! This invasive species is an incredibly aggressive grower, able to sprout from a mere portion of a leaf, and able to withstand flooded root systems for many years. While the flowers are a brilliant showy, white, stands of Japanese knotweed create a major issue for riparian biodiversity, as well as overall stability.
Though the leaves are much smaller and numerous than Japanese Knotweed, from afar these two plants could easily be confused. Goat’s beard is a less aggressive grower, and only grows to about 6 feet tall. If you like the look of Japanese knotweed, consider planting goat’s beard, which also tolerates moist soils.
Photo by Megan Hansen
If you spot Herb Robert, you’ll likely spot a lot of it. This pervasive understory plant will spread aggressively across the forest floor, creating large but sparse swathes of small purple flowers. Also known as “Stinky Bob,” this plant also produces chemicals that prevent other herbaceous plants from thriving. When removing, it’s important to make sure all plant material is disposed of carefully and off-site.
Photo by Joli Borah
Shiny geranium is quite similar to its relative, Herb Robert, but as its name suggests is shinier. It is also more limited to shadier sites, and has reddish, non-hairy stems. Leaves have 5-7 lobes which are shallowly lobed themselves, unlike the deeply lobed leaves of bleeding heart.
A landscaping favorite of the PNW, bleeding heart has distinct, heart shaped pink flowers. However, before flowering, the leaves look quite similar to Herb Robert. Before flowering, you can distinguish bleeding heart from Herb Robert by checking for hairs, and crushing the leaves to smell them. Bleeding heart is hairless where Herb Robert is hairy, and has no odor unlike “Stinky Bob.”
Photo by Steve Sullivan
This understory plant is classified as a regulated Class A Noxious Weed by King County, due to its ability to aggressively spread. You can identify it by its triangular, toothed leaves that smell like garlic when crushed; or by the small white flowers. It tends to grow in bunches, and typically around two to three feet tall.
Photo by Hans Braxmeier
Fringecup is a lovely Northwest native groundcover, that is often mistaken for Garlic mustard to its heart-shaped, toothed leaves and tall flower stalks. However, fringecup has flowers running up the curved flower stalk, while garlic mustard just has white flowers at the top of the stalk. Additionally, fringecup leaves tend to be more clustered towards the base, as opposed to running up the length of the stalk. Fringecup is frequently used as groundcover in restoration!
Photo by Megan Hansen
Similar to garlic mustard, largeleaf avens has a tall, alternately leaved stalk with a small cluster of flowers on top. However, largleaf avens has yellow flowers, and the leaves are more distinctly three lobed. Additionally, this plant lacks the odor of garlic mustard.
You’ll want to watch out for poison hemlock, since it’s not only highly toxic, but also very invasive. It is a relatively common plant, found on roadsides, trails, fields, parks, and around homes and gardens. You can identify it by its fern-like, finely divided leaves with a musty, unpleasant smell. The stems grow up to 6-10 feet tall, and are bright green with reddish/purplish spots and streaks. They also have tiny, white flowers clustered in umbrals.
Photo by Rasbak
This is another highly invasive, highly noxious weed that is deeply hazardous to human health. Contact with the sap can produce scarring burns. Giant hogweed is also a class A regulated noxious weed, and you should contact King County Noxious Weed if you find this huge invasive. The stalks have coarse white hairs, purple spots, and the can grow up to 5 feet tall.
Photo by Marie Claire
More commonly known as Queen Anne’s Lace, this look-alike is invasive, but is unregulated and not as pervasive as the other invasives listed in this category. Wild carrot also poses no threat to human health, though it is mildly toxic to livestock. Unlike giant hogweed and poison hemlock, it has no purple coloration on its stalks, and has very fine hairs. It also grows much shorter than hemlock or hogweed, reaching a height of around 3 feet at a maximum.
Photo by J Rosenberry
This native northwest wildflower loves wet, roadside ditches. Though it is native, it still poses a hazard to human health; the sap can cause rashes and burns similar to that of giant hogweed. You can distinguish cow parsnip from poison hemlock and other look alikes by its smaller, less divided leaves. It also has a thicker, more rigid stem with white fuzzy hairs. The flower clusters also tend to be wider on the whole.
Photo by Jane Shelby Richardson
Thanks for Reading!
We hope you enjoyed our brief pointers on invasive plant look-alikes and how to tell them apart. If you are getting involved in any restoration projects, make sure to keep an eye out for these species! If you’re looking to do some landscaping, we encourage you to use native plants, which have so many benefits for local pollinators and wildlife, and are just as beautiful!
Have you been bamboozled by these look-alikes before? Know any other similar species that have tricked you in the past? Feel free to comment your stories about plant doppelgangers, we’d love to hear your stories!
Lastly, if you’re interested in learning more about these invasive species, and how their management is prioritized by the county, click here to find out about their classification.
Fate is an Americorps member with Forterra, and proud to be part of the Green Seattle Partnership. He studied plant ecology at Vassar, where he worked on the Preserve there. Following a year with an eco-landscaping group in the Hudson Valley, he returned home to Seattle to see the trees of his childhood. As of today, he primarily works to support Green City Partnerships and riparian restoration efforts in the Puget Sound.